implementation of iptables

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Basic Rule Management:

Copysudo iptables -L                    # List rules in filter table
sudo iptables -L -n                 # List with numeric output (no DNS lookup)
sudo iptables -L -v                 # List with verbose output (packet counts)
sudo iptables -t nat -L             # List rules in NAT table

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To stop every single packet from going in/out of your system. For security reasons, make sure to do this so that no other packet that you explicitly specify, is going to be transferred.

Copysudo iptables -P INPUT DROP
sudo iptables -P OUTPUT DROP
sudo iptables -P FORWARD DROP

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To allow packets inside your loopback interface to travel without problem.

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These commands allow DNS and DHCP traffic:

DNS Rules (Port 53):

Copyiptables -A OUTPUT -p udp --dport 53 -j ACCEPT
iptables -A OUTPUT -p tcp --dport 53 -j ACCEPT

• Allow outgoing DNS queries to DNS servers

• Port 53 is the standard DNS port

• UDP is most common for DNS, TCP for large responses

• Enables your computer to resolve domain names (google.com → IP address)

DHCP Rules (Ports 67-68):

Copybashiptables -A INPUT -p udp --dport 67 -j ACCEPT
iptables -A INPUT -p tcp --dport 67 -j ACCEPT
iptables -A OUTPUT -p udp --dport 68 -j ACCEPT
iptables -A OUTPUT -p tcp --dport 68 -j ACCEPT

• Port 67 (INPUT): Allow incoming DHCP responses from DHCP server

• Port 68 (OUTPUT): Allow outgoing DHCP requests to DHCP server

• Enables automatic IP address assignment from your router/network

What happens without these rules:

• No DNS: Can't resolve website names, only IP addresses work

• No DHCP: Can't automatically get IP address from router

• Network breaks: Most internet functionality stops working

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